Heat carrier for high temperatures



Patented Dec. 18, 1934 HEAT CARRIER FOR HIGH TEMPERATURES Karl Gensch,Berlin, Germany, assignor to Gesellschaft fiir Drucktranslormatoren(Koenemann-Transformatoren) G. m. b. 11., Berlin, Germany, a corporationof Germany No Drawing. Application May 24, 1933, Serial No.

672,734. In Austria May 30, 1932 m.

8 Claims.

The invention relates to a heat carrier for high temperatures forindirectly heated plants. While I prefer the illustrative salt meltembodiments disclosed herein, which are particularly desirable becauseof their cheapness and efiectiveness, my invention contemplates, and mypreferred embodiments are illustrative of, such like substances as willbe suggested to the skilled chemist by my present specification. A saltmelt consisting of zinc chloride and several other metal chlorides whichform double salts with zinc chloride, was found to suit very well theaforesaid purpose.

Chiefiy a melt is used which contains approximately zinc chloride, 10%sodium chloride, and 15% potassium chloride. This melt has allproperties which are required from such a heat carrier, e. g. lowmelting point, high boiling point, good heat transfer, low viscosity,high specific heat, low specific weight; and last but not least it isvery cheap. Besides it does not attack iron, is not combustible, notexplosive, and does not form any explosive mixtures with othersubstances. The composition being as stated above, the melting pointranges approximately at 180 centigrade. If the melting point is desiredto be lower, it can be reduced to approximately 140 centigrade by addingother salts such as lithium chloride and ferric chloride. Compared toother heat carriers known so far, the above heat carrier offers thefollowing advantages.

It is much cheaper than any metal melt. Metals with low melting point,such as mercury or bismuth alloys, cost approximately from ten to twentyReichsmarks per kilogram. Their specific weight amounts approximatelyfrom 10 to 13. The chloride melt can be supplied at a price of one halfReichsmark per kilogram and has a specific weight of approximately 2.The metallic filling of an apparatus would cost approximately -260 timesas much. Even if comparatively cheap metals, such as lead and zinc, areused, the filling'still would cost approximatly fouftimes as much. Now,the melting point of these metals ranges above 300 centigrade, and this'fact renders operation conditions so difiicult that these metals cannot be used. Also the high coefficient of expansion and the goodconduction of heat of the metals in the solid state are of disadvantage.When the solid metals are heated they expand very much before gettingliquid; consequently, the apparatuses are stressed to such an extentthat they are liable to burst. Furthermore, the high specific weight ofthe metals has the disadvantage that if a high apparatus is used thelower parts of it are subjected to a considerably high hydrostaticpressure. Finally, several metal melts, e. g. molten zinc, attack ironvery much.

Oils having high boiling points, and other organic liquids, e. g.diphenyl oxide, can not be 5 used at temperatures over 400 centigrade.Up to the present no organic liquids are known which are stable abovethis temperature. They decompose, incrust the heating surface,especially in the highly loaded tubes, and then these tubes 10 burnthrough.

Compared to other salt melts, the above heat carrier has the specialadvantage that it is very cheap. Zinc chloride, sodium chloride, andpotassium chloride are by-products of very low price. Further the aboveheat carrier has such a low melting point that it can be melted byheating it by steam of customary pressure, e. g. 15 atmospheres. Besidesit contains neither water nor oxygen; therefore it does not attack iron20 even at high temperatures and cannot form any explosive mixtures withother substances, e. g. with coal, as is the case with nitrate melts.

The above heat carrier can be used especially in the chemical industryand in the oil industry, 25 in other words everywhere where heating athigh temperatures is involved, and where the products,

e. g. oil or other substances very sensitive to high temperatures, haveto be treated as gently as possible. 30

In the field of generation of high pressure steam, indirect heating bymeans of the above heat carrier offers great advantages. Under" theseconditions, the feed water treatment is not such an important factorbecause scale incrustations can only result in reducing the heattransfer, in other words in a decrease of efliciency; but never can theyresult in boiler explosions.

I claim:

1. An indirect heating system employing as the heat carrying medium amolten mixture of metal chlorides, predominantly consisting of chlorideof zinc, and including substantial quantities of metal chlorides of theclass consisting of alkali metal chlorides and chlorides having sim-"ilar effect in the molten mixture, the medium thus constituted having amelting point substantially below that of chloride of zinc.

2. An indirect heating system employing as the heat carrying medium amolten mixture of chloa ride of zinc and other metal chlorides formingwith chloride of zinc double salts existing in the molten mixture, themedium thus constituted having a melting point substantially below thatof chloride of zinc. 55

3. An indirect heating system employing as the heat carrying medium amolten mixture approximately '75% chloride of zinc, 15% chloride ofpotassium and 10% chloride of sodium.

5 4. An indirect heating system employing as the heat carrying medium amolten mixture of approximately '75% chloride of zinc, 12% chloride ofpotassium, 8% chloride of sodium, 5% chloride of lithium and 5% chlorideof iron,

5. An indirect heating system employing as the heat carrying medium amolten mixture preponderantly chloride of zinc, and containingsufficient alkali metal chloride to impart to the mixture a meltingpoint materi allynbglc w that of chloride of zinc. F m

\- 6:"An'indirectheating system employing as the heat carrying medium amolten mixture comprising preponderantly chloride of zinc, andcontaining sufficient metal halide of the class consisting ofpotassium-, sodium-, lithium-, and

iron-chloride to impart to the mixture a melting point materially belowthat of the preponderant metal halide.

'7. An indirect heating system employing as the heat carrying medium amolten mixture comprising preponderantly chloride of zinc, which is ahalide of a weak negative, acid forming metal, and sufiicient halides ofthe class consisting of NaCl, KCl and LiCl, which are halides of strongpositive, base forming metals, to impart to the mixture a melting pointmaterially below that of the preponderant metal halide.

8. An indirect heating system employing as the heat carrying medium amolten mixture comprising preponderantly chloride of zinc, which is ahalide of a weak negative, acid forming metal, having incorporatedtherewith at least one of the halides of the class consisting of NaCl,KCl or LiCl, which are halides of strong positive base forming metals,characterized in that one or more of the incorporated latter halidesforms with the preponderant halide a double salt existing in the moltenstate, and further characterized in that the quantity of these latterhalides present is sufiicient to impart to the mixture a melting pointmaterially below that of the preponderant metal halide.

KARL GEN'SCH.

